Conventional stretcher/lappers are known, for example from DE-B-1,927,863, and in these an unwinding carriage executes transverse to-and-fro movements above an exit conveyor movable at a constant speed.
When the unwinding carriage is at either one of its ends of travel, it has to stop in order to change its direction of movement, while it continues to unwind the web onto the exit conveyor at an unchanged speed. However, since the relative speed between the carriage and the exit conveyor has decreased greatly since it no longer comprises the transverse component of the movement of the unwinding carriage, the web is unwound in excess. These traditional machines thus produce considerable lateral bolsters which subsequently have to be eliminated in order to obtain a product having per unit area a weight which is approximately uniform at all points of its width.
It is known from FR-B-2,234,395 to overcome these disadvantages, on the one hand, by imparting to the exit conveyor a speed which varies in proportion to the absolute value of the speed of the unwinding carriage, particularly in such a way that the exit conveyor is at a stop when the unwinding carriage is itself at a stop during its changes of direction of movement, and on the other hand by giving the feed carriage located upstream of the unwinding carriage a law of movement such that the unwinding carriage delivers the web at a speed which is itself proportional to the speed of the exit conveyor and to the absolute value of the speed of the unwinding carriage.
Thus, the quantity of web deposited per unit area of the exit conveyor is theoretically constant, and consequently the lapped product produced is theoretically perfectly uniform.
Moreover, as a result of the lapping operation, the initially longitudinal fibers of the web feeding the stretcher/lapper are arranged transversely in the lap at a particular angle of inclination, for example less than 15.degree.. A result of this is that the tensile strength of the lap is much lower in the longitudinal direction of the lap than in its transverse direction which virtually coincides with the orientation of the fibers. This is a disadvantage because the lap is an intermediate product intended to undergo subsequent conversions, especially by needling, in the course of which it is pulled in its longitudinal direction. It is therefore in the longitudinal direction that the highest tensile strength would be desired. The poor tensile strength which has to be allowed for at the present time in order to conduct the needling or such like operations limits the working speed and brings about a transverse shrinkage during the needling, this shrinking tending to generate overthicknesses at the edges.